The determination of the distance, or range, of an object is relevant to a variety of applications. Efforts are constantly being made to improve the accuracy of rangefinding devices while maintaining manufacturing costs as low as possible.
It is known in the art to provide rangefinding devices which send a precisely timed light pulse toward an object and to make gated measurements of the light reflected thereby. The round-trip time of flight of the light pulse is simply related to the range of the object through the relation R=V×ΔtD/2, where R is the range of the object, V stands for the velocity of light in the medium through which it propagates and ΔtD is the time delay between the pulse emission and its detection.
Several rangefinding devices that include time-gated detection schemes are known in the art. For example, U.S. Pat. No. 5,081,530 (MEDINA) teaches a three dimensional camera including a rangefinder. The rangefinding application sends a light pulse toward a target and records the reflected light using two gated time intervals, one synchronized with the emission of the light pulse and the other starting at the end of the pulse. The range of the object is determined by the difference between the integrated energy in both pulses, normalized by the sum of these two energy values. More recently, MEDINA et al. reported in a paper entitled “Compact laser radar and three-dimensional camera” (J. Opt. Soc. Amer. A, Vol. 23, pp. 800-805, (2006)), a similar detection scheme combined with a scaling of a range register according to a calibrated factor.
Also known in the art is U.S. Pat. No. 7,095,487 (GONZALES-BANOS et al.). GONZALES-BANOS discloses systems and methods for determining depth using shuttered light pulses. A light emitter emits a pulse of light that is directed toward an object, where it is reflected toward a beam splitter. The beam splitter splits the reflected pulse into multiple pulses, with each pulse directed to a shuttered sensor with a different timing. The shuttered sensors measure the integrated intensity of the light, and these values are used to determine the depth of the object. A method is presented which calibrates a system that has an arbitrary number of shutters and enables the system to determine the depth of an object, even in the presence of ambient illumination and scattered light.
Other rangefinding systems and methods based on time-gated detection are for example taught in R. Miyagawa and T. Kanade, “CCD-based range-finding sensor”, IEEE Trans. Electron. Devices, Vol. 44, pp. 1648-1652, (1997), in S. Christie et al., “Design and development of a multi-detecting two-dimensional ranging sensor”, Meas. Sci. Technol. Vol. 6, pp. 1301-1308, (1995), and in U.S. Pat. Nos. 6,373,557 (MENGEL et al.) and 6,480,265 (MAIMON et al.).
There however remains a need in the field for a simple yet accurate rangefinding device which could be built using low-cost components.